Fluorescent lighting method and means



Feb. 9, 1965 SHAHEEN 3,169,213

FLUORESCENT LIGHTING METHOD AND MEANS Filed July 19. 1962 INVENTOR.

JOHN SHAHEEN ATTORNEYS United States Patent Ofiflce 3,169,213 FatentedFeb. 9, 1965 This invention relates to fluorescent lighting and moreparticularly to method and means for operating a plurality offluorescent or are dischargelarnps out of phase with each other and insuch a way as'to substantially eliminate stroboscopic effect or flicker.

The aforementioned flicker is present to a greater or lesser degree inall are discharge lamps and occurs when the current through the lampsupplying the excitation energy to the phosphor coating on the lampfluctuates and drops to Zero twice during each cycle of the alternatingcurrent generating source.

Efforts have been made to solve the problem of flicker by groupingaplurality of lamps together as a unit and operating them out of phasewith each other so that the intervals of reduced light intensity occurat different times for each lamp with the result that there tends to bea more uniform light emanating from-the three lamp unit. In largebuildings the phase differences between the several lamps of the unitare most commonly obtained by connecting each lamp of the lamp unitbetween different phases of a polyphase power source. phase power thatis distributed locally to the panel boards of commercial buildings is208 volts and derives from a three phase Y. connected source having 120between each phase and a grounded neutral, the light units consistedusually of three similar lamps all mounted in a single fixture andconnected respectively through three similar transformers in star ordelta to the three phases of the polyphase source delivering to thepanel board. While this means for obtaining strobe correction has beensatisfactory up to a point, particularly when lampshaving highlyretentivephosphor coatings areused,there still remains a substantialflicker which though not consciously apparent to the observer,'isdetectable by a photocell and does cause substantialstrainranddiscomfort to the eyes. This subliminal flicker is particularlydistressing to persons using their eyes constantly and for long'periodsof time under such light as, for example, while readingin a library orassembling small parts in a factory. I,

The aforementioned difficulty isbelieved to beduejto the fact thatalthough the potentials supplied to the three lamps'of the priorlighting units are 120 out [of phase with each other so that theirvoltage waveformsoverlap,

'there are still intervals of reduced voltage (and) current) Since mostpolyand across which the prior devices have been connected, it is foundthat the third, ninth, fifteenth, etc. harmonics cancel out and do notcontribute to the line voltages. Resultantly, there is a more pronouncedpeak at the points in each cycle where the voltage reaches its maximumand minimum and also a less rapid rate of change of voltage with time inthe regions where the voltage approaches zero.

and Where the fundamental is not reinforced by the above odd harmonics,particularlyrthe third harmonic; When the several line voltages of thethree phase source are observedtogether on an oscilloscope, there isstill seen to be a pronounced fluctuation in the envelope enclosing thethree line voltages and which is believed to account at least partiallyfor the aforementioned subliminal flicker. The priorstrobe correctedlighting apparatus of the type here concerned are disadvantaged alsobecause they require at least three electrical leads from the threephase source to the light fixture. three phase power may be available orbrought to a panel board in an existing building, usually the buildingitself is not wired for three phase (3 or 4 wire) distribution. Only twowires are available between the panel board and the individualelectrical fixtures or outlets. Consequently, a third wire must be runthroughoutthe building before these prior devices can be installed.This, of course, increases substantially the installation costs of andreduces the desirability as original or replacement equipment of theprior lighting apparatus. I have improved the art of fluorescentlighting by pro-. viding a simple lighting apparatus for mounting in asingle fixture and which-costs no more than prior comparable devices butwhich provides illumination of substantially uniform intensity and withsubstantially 'no subliminal stroboscopic effect or flicker. Under myinvention, .both

the coil voltages and the line voltages of the three phase;

Y connected source are used. These non-sinusoidalvolt ages are appliedto the several lamps of the unit and mm-.,

bine in phase relation and overlap in such away as when observedtogether to produce a more uniform voltage envelope and a more uniformillumination from thelightingunit. i 7 Further, the lighting apparatusof'this invention can be installed readily in existing buildings becauseit d oes not require athird wireto be run from the. panel board or otherthree phase source to the fixture. This is because, in practice and asmentioned "previously, all low or fluctuations in the voltage envelope,between' adjacent voltage maxima and minima during each cycleofoperation. Consequently, there are also intervals wherein reducedexcitation'energy is supplied to the phosphorjcoating of and resultingin intervals of reduced light intensity from one or more of the lamps ofthe unit. I

' As mentioned previously, prior strobe corrected fluorescent lightingapparatus have been connected in star or delta to the several phases orin other words to obtain the line voltages from a grounded three phase Yconnected source found locally. Thislocal powerultimatelyderives from athreephase generating device which, inpractice, is not an idealalternator andwhich generatesin ,each of its windings a coil voltagewhich is not sinusoidal but which is rather the sum of a fundamentalwaveplus the odd harmonics. The' resulting coil voltage waveforms havemaxima and minima which are flattened andfmade wider and the rate ofchange of voltage with time is substantially increased in the regionsWhere the voltages approach zero. On theothenhani when calculating theline voltages or voltages between the phases generated by such "asource, I

lamps 14, '15. I 5 H p Y Under my invention, a third autotransformer 16is;

voltage (under 300 v.) three pliase'Y connected distribution circuitsare required to be grounded at the pole; Thus ground canfunction'eifectively'as the third conductorbetween, my lighting unit andthe power source. Accordingly, to. effect strobe correction, the circuitofmyap paratus may simply be connected to the conventionally groundedlight fixture or junction boxinwhich "the unit itself ismounted. 7 1 1In the illustrated embodiment: j I p j The figure of the drawing is adiagramaflerepresenta tion of my improved strobe corrected threelarnplighting unit connected at a panel board to two: phases ofa groundedthree phase Y connected generating source." 1

Referring to the drawing, my improved lighting appanatus comprises apair of similar autotransf or'mers'm,

11 having their low voltage terminals 12,13 respectively connectedtogether and to the low potential ends of 'afpair of conventional singlephase self-starting fluorescent lamps 14, 15 which may be type 96Tl2,for example, requiring fortheir operation a potential of approximately630- volts. Transformers 10, "ll have also high voltage rer: minals 6, 7connected respectively through; inductive the high tentiaI eridSf orelements or chokes 8, 9 to More particularly, although provided alsowhich is different from the aforementioned transformers if), 11 :as willhereinafter be described more particularly. Autotransformer 16 has itslow voltage terminal 18 connected to the intermediate voltage terminal19 of autotransformer it and its intermediate voltage terminal 20connected to the intermediate voltage terminal 21 of autotransformer 11.A third fluorescent lamp 22 similar to lamps 14, 15 is connected acrossthe full winding of autotransforrner 16 and has its low potential endconnected to the low voltage terminal 18 and its high potential endconnected through inductive element or choke 23 to the high voltageterminal 24 of autotransformer 16. Thus the primaries of transformers 1f11 are connected together in series and the series combination isconnected in parallel with the primary of autotransformer 16.

A conductor id is provided for connecting the inte mediate voltageterminal 19 of autotransformer to panel board 26 and more particularlyto the panel board terminal indicated at A delivering one phase, sayphase A of a three phase Y connected alternating potential source 29.Also a conductor 27 is provided for connecting the intermediate voltageterminal 21 of transformer 11 to the panel board terminal indicated at Bdelivering another phase, sa'y phase B, of said alternating potentialsource 29. It will be understood, however, that the conductors '25, 27can just as well be connected to phase A and phase C (indicated at C onthe panel board) respectively or indeed to any two different phases ofthe alternating potential source 29.

A third conductor 28 may be connected between the low voltage side ofautot'ransformers 10, 11, say at 13, to the panel board 26 and moreparticularly to the neutral terminal indicated at N therein, whichterminal is, as mentioned previously, always grounded in' low. voltagedistribution circuits. or more preferably and if as usual the electricaloutlet in which the lamp unit is to be mounted isgrounded, the circuitat point 13 may simply be grounded to that outlet.

In the usual commercial balanced three phase generator, three equal coilvoltages, that is voltages between the phases and the neutral areproduced across the several Y connected coils and these voltages are,120 out of phase with each other. The coil voltages add vector ially toproduce three equal line voltages, that is voltages between the severalphases, which are also 120 out of phase with each other and advanced 30with respect to the aforementioned coil voltages. And for these balancedthree phase generating sources, the linevoltage is found to be V? timesthe coil voltage. The aforementioned relationships pertain also to thethree phase power distributed locally to the panel board 26, and inpractice the potential between phases A, B or C and N is approximately120 volts while the potential between any two of phases A, B, C isapproximately 208 volts.

It is a feature of this invention that my lighting apparatus utilizesboth line and coil voltages to power the several lamps of the unit formore effective strobe correction. More particularly, two of the threesimilar lamps of the unit, namely lamps 14, are connected through theirrespective similar autotransforme'rs 10, 11 across the panel boardterminals A, N and B, N respectively. The potentials across the lamps,therefore, derive ultimately from two different coil voltages producedin the generating source 29 and are equal in magnitude and 120 out ofphase with each other. Also as mentioned previously, the coil voltagesare non-sinusoidal and contain in addition to the fundamental, the oddharmonics particularly the third which tends to oppose the fundamentalat its maximum and minimum points and to reinforce the fundamental atthe points where that approaches zero amplitude thereby producingvoltage waveforms having flattened maxima and minima and short intervalsof reduced voltage at alternation.

Further in accordance with the invention, the third lamp 22 provided ineach unit is connected through its transformer 16 across the panel boardterminals A, B. The third lamp is thus powered by the line voltagebetween phase A and phase B of the generating source 29 which voltage isout of phase with and exceeds by a factor of V? the aforementionedvoltage between terminals A, N and B, N. Also it contains no tn'plen(third, ninth, fifteenth, etc.) harmonics for reinforcing thefundamental at the points where that approaches zero amplitude and foropposing the fundamental at its maxima and minima. To accommodate thevoltage differences and in order to provide the same potential acrosseach of the similar lamps 14, 15, 22, the transformation ratio ofautotransformer 16 is made approximately times the transformation ratiosof autotrans'formers 10, 11. For the usual commercially distributedpower, then, autotnansformers 1f 11 may be standard volt ballasttransformers while autotransformer 16 may be a 208 volt transformer.

Thus when my lighting apparatus is connected as above, the potentialsacross the three lamps l4, 15, 22 are out of phase with each other andequal in amplitude. But the potentials across lamps 14, 15 only arealtered as described particularly by the third harmonic, while thatacross tube 22 is not affected by said third and the other triplenharmonics. With the aforementioned differences in the shapes of and thephase relations between the several voltages powering the several lampsof the unit, these voltage waveforms when observed together are found tobe contained in a more uniform voltage envelope and there is produced inthe three lamp unit a light of uniform intensity and with substantiallyno stroboscopic effect or flicker.

Further, the three lamp lighting unit of this invention requires in theusual situation only two wires fr'omthe unit to the panel board. Thatis, if as usual the junction box or outlet in which the unit isinstalled is already grounded, the third electrical lead 28 may beeliminated and the circuit grounded at 13 to the fixture. Thus theinstant apparatus may be installed readily and inexpensively and with noadditional wiring as replacement equipment in existing building outlets.For a nearly balanced power factor for most efficient operation of theoverall installation, the three lamp units of this invention aredesirably installed in groups of three, with each unit being connectedto different phases at the panel board 26. Thus the first unit isconnected to terminals A, B, the second unit to terminals B, C and thethird unit to terminals C, A. And of course, more than one unit may beconnected in the several groups.

I claim as my invention:

1. Lighting apparatus comprising: first, second, and third transformers;corresponding first, second, and third are discharge lamps connectedacross the secondaries of said transformers; a generator having Yconnected coils; electrical connections between the primary windings ofsaid first and second transformers at one terminal thereof and thecommon terminal of said coils; electrical connections between theprimary windings of said first and second transformers at the otherterminals thereof and the other terminal respectively of first andsecond ones of said coils, and electrical connections connecting theprimary of saidthird' transformer across said first and second ones ofsaid coils.

2. Lighting apparatus comprising: three transformers; three similar arcdischarge lamps; means for electrically connecting the secondaries ofsaid transformers respectively to said lamps, the primaries of two ofsaid transformers being connected together in series, the primary of theother of .said transformers being connected in 3. Lighting apparatus formounting in a single fixture comprising: three autotransformers; threecorresponding similar are discharge lamps; eiectrical connectionsbetween ea'ch of said lamps at one end thereof and the high voltageterminal of its corresponding autotransformer; electrical connectionsbetween each of said lamps at the other end thereof and the low voltageterminal of its corresponding autotransformer, two of said autotransformers having substantially equal voltage transformation ratios, saidratios being approximately equal to /3 times the transformation ratio ofthe other of said autotransformers; an electrical connection between thelow voltage terminals of said two of said autotransformers; and meansfor connecting the intermediate voltage terminals of said two of saidvantotransformers respectively'to the low voltage and the intermediatevoltage terminals of the other of saidautotransforrners.

4. Lighting apparatus for mounting in a single fixture comprising: threeautotransformers; three corresponding similar arc discharge lamps, eachofsaid lamps being connected at one terminal thereof through a reactiveelement to the high voltage terminal of its correspondingautotransformer, each of said lamps being'connected also at the otherterminal thereof to the low voltage terminal of itscorrespondingautotransformer, two of said autotransformers having substantially equalvoltage transformation ratios, said ratios being approximately equal to/3 times the voltage transformation ratio of the third of saidautotranstormers; means for connecting the low voltage terminals of saidtwo of said autotran-sformers to each other and means for connecting theintermediate voltage terminals of said two of said autotransformersrespectively to the low voltage terminal of the third of vterminalfofvsaid third of said autotransformers.

5'. Lighting apparatus for mounting in a single fixture comprising:three autotransforrners, two ofsaid autotransformers havingsubstantially equal voltage 'trans- 0 formation ratios, said ratiosbeing approximately equal lto 3 times the voltage transformation ratioof the third of said autotransformers; three corresponding similar arcdischarge lamps connected across the full windings of saidautotransformers; electrical connections between the low voltageterminals of two of said autotransformers and ground and electricalconnections between the intermediate voltage terminals of said two ofsaid autotransformers and the primary of said third of saidautotranoformers. r V

6. A lighting system comprising a plurality of lighting units, each ofsaid units containing three transformers, two of said transformershaving their primaries connected together in series and having,substantially equal voltage transformation ratios, the third of saidtransformers having its primary connected in parallel with the primariesof said two'of said transformers and having a voltage I transformationratio equalrto substantially the 7 r times said ratios of said two ofsaid transformers.

References Cited by the Examiner I UNITEDSTATES PATENTS 2,683,798 7/54Craig 315-144 X 2,996,644 8/61 Nathanson 315-438 3,027,490 3/62 Craig315-144 3,032,682 5/62 Lord 315--144 DAVID J. GALVIN, Primary Examiner.

JAMES D. KALLAM, Examiner.

1. LIGHTING APPARATUS COMPRISING: FIRST, SECOND, AND THIRD TRANSFORMERS;CORRESPONDING FIRST, SECOND, AND THIRD ARC DISCHARGE LAMPS CONNECTEDACROSS THE SECONDARIES OF SAID TRANSFORMERS; A GENERATOR HAVING YCONNECTED COILS; ELECTRICAL CONNECTIONS BETWEEN THE PRIMARY WINDINGS OFSAID FIRST AND SECOND TRANSFORMERS AT ONE TERMINAL THEREOF AND THECONNON TERMINAL OF SAID COILS; ELECTRICAL CONNECTIONS BETWEEN THEPRIMARY WINDINGS OF SAID FIRST AND SECOND TRANSFORMERS AT THE OTHERTERMINALS THEREOF AND THE OTHER TERMINAL RESPECTIVELY OF FIRST ANDSECOND ONES